The present invention relates to an optical assembly, preferably a liquid-lens-optical assembly, which is equipped with a liquid lens, and an optical-information-reading device which is provided with this liquid-lens-optical assembly.
A bar code, which is one-dimensional code information for use in merchandise control, stock management or the like, has been well known. A two-dimensional code has also been known, as the code that has increased information density. Also known is a method of capturing the two-dimensional code with a solid-state image sensing device such as a CMOS image sensor or a CCD image sensor, as a device reading the two-dimensional code, performing various kinds of processing on such an image and binarizing and decoding.
The CMOS image sensor to be used in a device for reading such code information is no different in function from that with which a digital camera, or the like, is equipped so that it functions similarly to a photographer shooting an object, a scene, or the like. For example, in a case of stock management or the like, it is used for photographing both the object of interest and a location where the object is housed and storing them together with code information on a database.
Further, most portable phones are equipped with a small-sized camera using the above-mentioned CMOS image sensor. The greater part thereof not only has a camera function of the portable phone to photograph a scene or a figure, like a common digital camera, but often also includes a bar code/two-dimensional code scanner and an OCR (optical character reader).
There is a need for a focusing configuration in a device for shooting an image with a solid-state image sensing device, or an automatic focusing configuration, a so-called autofocus function. For the autofocus function, moving a location of a lens along an optical axis mechanically has been known, but it is difficult for a small sized device such as a portable phone to be equipped with such a mechanism. Thus, there is a need for configurations where a lens itself has an autofocus mechanism. As one of them, a liquid lens has been known.
FIG. 8 is a configuration diagram illustrating a liquid lens conceptually. The liquid lens 100 is configured so that water solution 101 having high conductivity and insulating oil 102 are sealed in a container 103 that has two opposed surfaces, each of which has a light-permeable transparent window. The liquid lens 100 is provided with an electrode 104a that contacts the water solution 101 and an electrode 104b that contacts the water solution 101 and the oil 102 both through an insulating portion. When the electrodes 104a, 104b are electrically charged to apply voltage to the water solution 101, a configuration of an interface 105 between the water solution 101 and the oil 102 may be altered. Such a phenomenon is referred to as “electrowetting phenomenon”. It is possible to move a focus position of lens 100 by altering a curvature of the interface 105 between the water solution 101 and the oil 102 so that light passing through the lens can come into focus at different distances from the lens.
Such liquid lenses have been applied to a camera module, a code scanner, and the like, as disclosed, for example, in Patent Document 1 (see below). Providing a temperature sensor to perform a temperature-compensating focusing control has also been disclosed (for example, see Patent Document 2). Further, providing a cooling mechanism for a liquid lens has been disclosed (For example, see Patent Document 3).
Patent Documents
Patent Document 1: Japanese Patent Application Publication No. 2005-259128.
Patent Document 2: Japanese Patent Kouhyou Publication No. 2008-511042.
Patent Document 3: Japanese Patent Application Publication No. 2008-304792.
A camera module with a liquid lens is provided with parts which constitute a heat source, such as a driving part of a solid-state image sensing device. The liquid lens, having voltage applied thereto is configured so that curvature of its interface varies because of temperature variation, thereby requiring temperature-compensation, as in patent document 2. However, it is difficult to mount a temperature sensor on the liquid lens itself because the liquid lens is small, its diameter being about several millimeters. On the other hand, if a temperature sensor were mounted on a substrate mounting the solid-state image sensing device, it is susceptible to any heat generated in other electric parts, so that it is impossible to detect temperature correctly.
Patent document 3 provides a cooling mechanism transferring heat to the outside using two temperature sensors and two peltiert elements around the liquid lens, but configuration is complex so that a mechanism relating to temperature detection and/or cooling occupies a large mounting area.
Further, in a popular camera, a technology is proposed in which images are captured in succession and decoding is performed on only focused images, but it takes a lot of time to capture the images up to the decoding thereof so that it may not be applied to a code scanner that manages articles and/or goods.
The present invention solves such a problem and has an object to provide a liquid-lens-optical assembly which can detect temperature of a liquid lens appropriately with a simple configuration to cope with a temperature changes, and an optical-information-reading device which is provided with this liquid-lens-optical assembly.